1. Technical Field
The present invention relates to a catheter system for continuously measuring the centrovenous oxygen saturation and/or measuring the local concentration of injected indocyanine green, in particular, catheter systems having a flexible, elongated, centrovenously applicable basic body, a fiber-optic probe for taking reflecto-oximetric measurements, a fiber-optic lumen for housing the fiber-optic probe and fastening means to prevent a longitudinal shift of the fiber-optic probe relative to the fiber-optic lumen, the fastening means being detachable to allow a longitudinal shift of the fiber-optic probe relative to the fiber-optic lumen for removal of the fiber-optic probe.
2. Description of Related Art
In the surgical field and in intensive medicine, centrovenous catheters (CVC) with several lumina, so-called multilumen CVC, are positioned which serve to                measure the centrovenous pressure,        simultaneously supply infusion solutions, blood and blood derivatives as well as pharmaceuticals via lumina, and        take blood samples for blood/gas analytical, hematological and biochemical analysis.        
Within the scope of centrovenous blood/gas analysis, the centrovenous oxygen saturation (ScvO2) is of particular interest since valuable information about the oxygen-availability and oxygen utilization of the entire organism can be obtained from it. A lowering of cardiac output, a reduction of the oxygen carrier hemoglobin, a reduced oxygen supply by artificial respiration or an uncompensated increase in the oxygen consumption of the organism can be quickly determined by means of a fiber-optic centrovenous catheter from a decrease of the centrovenous oxygen saturation by continuously monitoring the centrovenous oxygen saturation. In this respect, the continuous monitoring of the centrovenous oxygen saturation is suitable as a cost-efficient, global physiological monitoring method. The centrovenous oxygen saturation can be measured in the flowing blood by means of fiber-optic reflecto-oximetry at a measuring wavelength of about 660 nm. Optical radiation of another wavelength of usually about 930 nm is used as a so-called reference wavelength. At this wavelength, there is no substantial difference between the reflection of oxygenated and oxygen-free hemoglobin. The measurement result at the reference wavelength is used to compensate flow-dependent and other artifacts. However, measuring errors can occur in the presence of the diagnostic agent indocyanine green, which is sometimes introduced into the blood stream, since indocyanine green absorbs to varying degrees at 660 nm and 930 nm.
A liver function test is performed by means of indocyanine green (ICG) in many critically ill patients in the surgical field and in intensive medicine. Indocyanine green is a well-tolerated pharmaceutical which binds immediately to plasma proteins after it has been intravenously administered, remains primarily in the blood system and is only discharged unaltered into the gall bladder by the liver with a normal half-life period of 3-4 minutes. Indocyanine green can be continuously measured by means of fiber-optic reflection densitometry at a wavelength of about 805 nm. In this case, optical radiation at about 900 nm can be used as reference wavelength. In particular in critically ill, hemodynamically unstable patients, it is especially important to be able to perform the continuous measurement of the centrovenous oxygen saturation during the liver function determination by means of indocyanine green.
A catheter system for continuously measuring the centrovenous oxygen saturation, in which however fiber optics are fixed permanently in a multilumen CVC, contrary to the catheter system of the aforementioned type, is known from the U.S. Pat. No. 5,315,995. The fiber-optic bundle which is used to measure the centrovenous oxygen saturation ends directly at the distal end of the catheter. In this case, the distal end has a flat surface, the catheter is, in a way, cut off at a right angle relative to the catheter shaft. Due to the relatively large distal surface and due to a lack of a tapering tip, the catheter cannot be placed by means of the so-called Seldinger technique. This refers to a method in which, after the blood vessel into which a catheter is to be inserted has been punctured, a thin guide wire generally being about twice the length of the distal lumen (=channel whose end is furthest away from the examiner) which ends centrally relative to the round cross section at the tip of the catheter is advanced in the blood vessel via the puncture cannule. After the guide wire has been advanced, the puncture cannule is removed by pulling back via the wire. A so-called dilator, a relatively robust and rigid, single-lumen catheter made of a plastic material and having a distal tip tapering to the diameter of the guide wire, is then advanced in the vessel via the guide wire. The purpose of the dilator is to expand the puncture channel through skin, fat and muscle tissue and the blood vessel wall to the diameter of the catheter. After expansion, the dilator is removed, the guide wire remains in the blood vessel with the distal tip. The free proximal (=closest to the examiner) end of the guide wire is now inserted into the tip of the catheter also tapered toward the guide wire diameter and advanced into the blood vessel via the guide wire. As soon as the catheter is correctly positioned, the guide wire is pulled out of the so-called distal lumen; thus, the distal lumen of the catheter is available for other uses.
On the other hand, the multilumen CVC known from U.S. Pat. No. 5,315,995 can only be advanced into the correct position in the central vein system by a previously placed lead-in catheter, a so-called introducer. This method is complicated and time-consuming; moreover, of course, the introducer has a considerably larger outside diameter than the multilumen CVC to be inserted. For this reason, there is a disadvantageous vessel puncture associated with greater risks together with a larger diameter than would otherwise be required for placing a multilumen CVC with the Seldinger technique. Furthermore, the known catheter system cannot be used to measure the indocyanine green concentration in the blood.
A catheter system of the aforementioned type for continuously measuring the centrovenous oxygen saturation is known from the U.S. Pat. No. 5,673,694. It describes a fiber-optic probe and a fiber-optic catheter with a continuous lumen extending parallel to the fiber-optic lumen for continuous cleansing of the fiber optic ending in the area of the distal tip. The catheter system has a flexibly adjustable length of the part of the fiber-optic probe which is inserted in the distal lumen of the already inserted multilumen CVC. Since the fiber-optic probe can be flexibly advanced in its length by means of a frictionally connected locking device, the part of the fiber-optic probe or the fiber-optic catheter, respectively, situated outside of the multilumen CVC must be protected against bacterial contamination by means of a sterile cover. The previously known device has, in particular, the disadvantage that the fiber-optic lumen of the multilumen CVC into which the fiber-optic probe is inserted cannot, itself, be cleansed and thus there is the danger of the formation of blood clots at the distal outlet of the fiber-optic lumen. Furthermore, the known catheter system cannot be used to measure the indocyanine green concentration in the blood.